Artificial heart valves, which may be implanted in the human heart to replace natural valves, are essentially check valves which permit the flow of blood through the valves in a downstream direction, but block regurgitation of blood in a reverse or upstream direction. Heart valve prostheses typically fall into one of two categories--mechanical valves and tissue valves. The present invention finds its principal application in the field of mechanical valves, although it is not limited to this application as it may be used, for example, for tissue valves. Such mechanical valves generally include an annular valve housing or body having a central orifice which provides a passageway for blood. A valving mechanism, typically including occluders, is mounted in the orifice and opens and closes to regulate the passage of blood. One such valve which has enjoyed considerable success is disclosed in commonly assigned U.S. Pat. No. 4,276,658.
The outer circumferential surface of the valve body disclosed in the '658 patent includes a groove, which has facilitated the coupling of a suturing ring or sewing cuff to the valve body. The sewing cuffs for heart valve prostheses are generally a soft, flexible torus-like element through which sutures may pass to secure the sewing cuff, and consequently the heart valve, to the heart tissue.
Another method of coupling the sewing cuff to the valve body is shown in U.S. Pat. No. 5,071,431 to Sauter et al. Sauter et al. discloses a heart valve where a sewing cuff which is attached to a stiffening ring, with the stiffening ring being coupled to the valve body by a locking ring which rides in grooves in the outer periphery of the valve body and the inner periphery of the stiffening ring.
After a damaged or diseased natural valve structure is removed from the patient, the prosthesis is typically seated in the proper orientation and the sewing cuff is sewn to the peripheral heart tissue. Depending on the particular valve structure, care must be taken to ultimately orient the valve occluders to ensure that the valving mechanism is in the most favorable anatomical position to provide proper blood flow and to ensure that the valve operates without interference from surrounding heart tissue. This must either be done as the sewing cuff of the valve is sutured into place, or if the sewing cuff is rotatable relative to the valve, this can be done after the sewing cuff is secured to the heart tissue. While this latter arrangement is convenient and can obviate the need to remove and resuture a valve to effect a rotation, a rotatable valve must meet several criteria.
For example, the torsional force required to rotate the valve must be low enough so that the surgeon is able to rotationally position the valve with ease and without damage to the surrounding tissue. Once implanted, however, the valve body must maintain the desired position during the remainder of the surgery, and thereafter. Consequently, the torque required to initiate rotation must be great enough to prevent spontaneous in vivo rotation. Thus, the torsional force required to rotate the valve body within the sewing cuff should be predictable and fall within a narrow predetermined range such that it may be easily adjusted by the surgeon, yet be resistant to undesirable in vivo rotation once implanted. Moreover, the desired torque characteristics should be repeatable from valve to valve without significant variation.
The torsional force required to rotate the valve body relative to the sewing cuff will be determined by the manner in which the sewing cuff is retained on the valve body. Various methods have been proposed to rotatably secure the sewing cuffs of heart valve prostheses to the valve bodies. For example, U.S. Pat. No. 4,197,593 to Kaster et al. discloses a heart valve where a sewing cuff is sutured to a polymeric slip ring that slides along the surface of the valve body. U.S. Pat. No. 4,535,483 to Klawitter et al. discloses a heart valve where the sewing cuff is carried by deformable metal retainer rings which engage a stiffening ring disposed in and secured to a peripheral groove in the valve body. U.S. Pat. No. 5,104,406 to Curicio et al. discloses a heart valve where the fabric of the sewing cuff is stitched to a core, which directly abuts and rides the groove in the valve body; the core and the valve additionally sandwich the fabric along the annular space where the fabric is stitched to the core. U.S. Pat. No. 5,178,633 to Peters discloses a heart valve where the sewing cuff is coupled to the valve body by continuous fastener bands. The frictional engagement between the fabric tube and the valve body or "orifice ring" is controlled by the internal diameter of the fastener bands, which may be manufactured with precision. A need exists for an improved rotatable heart valve prosthesis.